1. Field of the Invention
The present invention generally relates to hydrometers and, more particularly, is concerned with a hydrometer for testing engine coolant fluid and indicating visually the concentration, or level, of antifreeze in the coolant fluid.
2. Description of the Prior Art
Hydrometers have been used for many years to test the freezing points of coolant fluids in motor vehicles. Traditionally, these hydrometers have utilized float tubes with appropriate internal scales that provide a reading of the freezing point based upon the specific gravity of the coolant fluid. Such hydrometers provide an accurate reading, but are relatively delicate and costly to construct and maintain.
Ball-type hydrometers have been developed for medical applications which use balls of different specific gravity to continuously measure the specific gravity of the fluid. When a ball of a known specific gravity floats at the surface of the fluid, it is known that the specific gravity of the fluid is greater than that of the ball. By identifying which balls float on the surface of the fluid, the specific gravity of the fluid can be identified within a given range. Examples of these ball-type hydrometers are disclosed in U.S. Pat. Nos. 3,626,763 and 3,631,727 to White.
Several recent ball-type hydrometers suited for use in automotive applications are disclosed in U.S. Pat. No. 4,649,747 to Barber et al, U.S. Pat. No. 4,702,109 to Viola, and U.S. Pat. No. 4,736,628 to Lin. The ball-type hydrometers of the Viola and Lin patents have similar constructions. These hydrometers include a generally rectangular housing defining a row of vertical cavities partially partitioned from one another so as to contain a plurality of balls of different specific gravities while maintaining fluid communication with adjacent cavities. The housing and the partitioned cavities therein are open at the top and disposed in fluid communication with inlet and outlet tubes rigidly connected at opposite ends of the housing. The tubes are adapted for connection to fluid lines in an automotive coolant system.
The Barber et al patent discloses several versions of a hydrometer for connection in an engine coolant flow line. One version has a T-shaped fitting, a generally cylindrical transparent view dome, a cap for attaching the dome to the fitting, and a plurality of float balls of different specific gravity contained in a chamber defined by the dome. The fitting is composed of a main branch and a center branch. The main branch defines a straight flow passage and opposite inlet and outlet ends adapted to be directly connected in the coolant flow line. The center lateral branch is located intermediately between the inlet and outlet ends of the main branch. The center branch defines a flow passage extending transversely to the straight flow passage of the main branch. The transparent view dome is attached by the cap to the center lateral branch of the fitting and is located above the fitting when the fitting is properly oriented in its installed position. Also, an air release valve is installed on the top wall of the view dome for use in releasing air which might be trapped in the top of the dome. Alternatively, a venturi vent tube is installed axially in the view dome for establishing communication between the top of the dome and the flow passage of the main branch to evacuate air from the top of the dome.
A drawback of this one version of the Barber et al hydrometer is that it requires periodic servicing to ensure that it is working properly. The float balls used in the Barber et al hydrometer to visually indicate the strength of the antifreeze in the coolant fluid are loosely contained within the chamber defined by the view dome. Thus, a circular screen has to be employed at the bottom of the dome to prevent the balls from settling downward through the flow passage of the center branch into the flow passage of the main branch where they would escape into the engine coolant line. It is the presence of the screen that necessitates performance of periodic maintenance be performed on the hydrometer to clean the screen. To check and clean the screen, the cap and dome of the hydrometer must first be removed and then replaced.
The drawback of requiring periodic maintenance is that oftentimes it will be overlooked and thus not be done by the vehicle owner. As a result, the hydrometer may fail to perform its intended function of providing an accurate indication of the antifreeze strength.
Consequently, a need still remains for improvement of hydrometer design in order to make it as maintenance-free and as accurate as possible.